Objectives of the proposed research are elucidation of 1) the molecular heterogeneity of the major density classes of plasma lipoproteins in humans under defined conditions of health and disease and in hyporesponder and hyperresponder rabbits and monkeys as a function of diet, 2) the composition and structure of molecular subspecies of the major density classes of lipoproteins, 3) the structure of the apolipoproteins, and 4) the roles of specific apolipoproteins in the interactions of dipoproteins and cells.